Embodiments of the present invention relates to capacitors and in particular to capacitors integrated in a semiconductor substrate.
Integrated capacitors are important elements in many semiconductor devices or integrated circuits. For example, integrated capacitors are used in PIN switches or filters. Moreover integrated capacitors are used in memory cells in conjunction with a transistor in order to store data information in the memory cells.
One aspect of capacitor design is to further increase the capacity value of capacitors. The capacity of a capacitor is generally expressed asC=∈A/T, 
where ∈ is the permittivity or dielectric coefficient, A is the area of the capacitor electrode and T is the insulator thickness. Accordingly, possibilities to increase the capacity include increasing the permittivity, e.g., by using high-k materials, reducing the insulator thickness T, and increasing the electrode area A.
However, typically, a second aspect has to be considered in capacitor design: the surface area available for the capacitor structure is limited. In particular in planar integrated circuit design a specific surface area is given for the layout or design of the capacitor, and the task is to provide, for example, a capacitor with maximum capacity using this given surface area of the substrate.
Thus, the task can also be described as increasing or optimizing the “specific capacity”, i.e., the capacity per surface area, e.g., measured in fF/μm2. The specific capacity is also referred to as “area capacity”.
Trench capacitors are one possibility to increase the specific capacity, or in other words, to increase the capacitor area A for a given substrate surface area. These capacitors are produced by creating vertical or almost vertical trenches or trench structures in a semiconductor substrate. The capacitor area A is defined by the “surface area” of the trenches within the substrate. As the capacitor area of these trench capacitors extends into the depth of the substrate it consumes less lateral or surface area of the substrate, and thus, allows to increase the specific capacity.
One possibility to generate capacitors with trench-structures is to etch the substrate such that individual “pillars” of the substrate remain after etching, to dope the substrate including the pillars, deposit a dielectric layer around the substrate pillars and to fill the trench structure around these pillars with a conductive material. The substrate and the pillars form one electrode, whereas the filled continuous trench structure surrounding the pillars forms the second or counter-electrode of the capacitor.
U.S. Pat. No. 7,030,457 B2, describes another conventional trench capacitor structure, where several individual trenches form one electrode of the capacitor, a doped substrate forms a second electrode of the capacitor, and wherein the trenches are electrically insulated from the doped substrate by a dielectric layer. U.S. Pat. No. 7,030,457 B2 uses regular patterns of trenches, where all trenches have the same distance between each other, independent of whether a substrate contact is arranged between these or not. For doping purposes for each substrate contact three trenches are sacrificed, i.e., created but not connected.